The correct answer is D - this is a compound sentence, which means it consists of at least two independent clauses, in this case they are: 1. The saber-toothed cat was a fierce and hardy hunter 2. It once roamed throughout North and South America. Independent clauses can exist. on their own, they are completed, as opposed to subordinate clauses.
B; Boorish means rough or coarse. Chaucer (the author) is saying that the Knight had never been rude, bad-mannered, or mean to another person. He is of high order among the other characters but chooses to be kind instead.